Illinois child support calculator

Since 2017 Illinois has used the income-shares model. Both parents’ monthly net income is combined, the basic support obligation is read from the state schedule, and each parent is responsible for the share that matches their percentage of the combined net income. The parent without the majority of parenting time pays their share to the other.

The basic obligation comes from the Illinois Schedule of Basic Child Support Obligations, published by Healthcare and Family Services and indexed by combined monthly net income (from about $854 up to $24,550) and the number of children. Illinois updates this schedule annually; this calculator uses the version effective March 20, 2026. Below the bottom of the schedule the self-support reserve and a minimum order apply; above the top the court uses the highest figure and its discretion.

To the basic obligation Illinois adds the child’s health-insurance premium and work-related child care, divided between the parents in proportion to net income (750 ILCS 5/505(a)(3.7)). This calculator adds the amounts you enter to the basic obligation before prorating.

When each parent has the child for at least 146 overnights a year (about 40%), Illinois uses the shared physical care calculation (750 ILCS 5/505(a)(3.8)): the basic obligation is multiplied by 1.5, each parent’s share is computed, and the amounts are offset by parenting time, usually lowering the order. Because that needs the exact overnight split, this calculator computes the standard obligation and flags when a shared arrangement likely applies.

It combines both parents’ net income, reads the current schedule, adds child care and health insurance, and splits the total by net-income share. It does not convert gross income to net for you, apply the self-support-reserve/minimum calculation below the schedule, run the shared-physical-care offset, or apply a deviation the court may order. For a figure you can file, use the official Illinois worksheet or consult an attorney.